PL190635B1 - Magnesium die casting process - Google Patents

Abstract

1. A method of pressure die casting of magnesium alloy in a semi-solid state in which melted magnesium alloy flows through a supply duct and injecting it into the mould cavity. It is characterised in that the stream of the alloy leaving the supply duct (26) is extended on the sides in controlled conditions against the direction of injection. The speed of the alloy stream flow in the supply duct (26) is within the range of 140-165 m/s and the speed of the alloy stream flow in the area of controlled extension is 25-50 percent smaller than the speed of the alloy stream flow in the supply duct (26). 6. Metal flow system in the magnesium alloy pressure die casting device in a semi-solid state, connected with a mould with a cavity, which has at least one supply duct between the source of melted alloy and the mould cavity. It is characterised in that the supply duct (26) is connected with at least one area of controlled extension with increasing cross-section area. The proportion of the cross-section area of the controlled extension area to the cross-section area of the supply duct (26) is between 2:1 and 4:1.

Description

The present invention relates to a magnesium alloy die casting process and a metal flow system in a semi-solid magnesium alloy die casting device.

190 635

It is believed in the die casting industry that due to the lower heat capacity of magnesium alloys compared to zinc and aluminum alloys, large feed channels and gates must be used to avoid premature solidification of the molten magnesium alloy. Indeed, this is considered the best practice by the industry, although interpretations vary widely.

Many different solutions are known to ensure satisfactory magnesium alloy casting. However, magnesium alloy die casting produced by these methods typically exhibit a greater degree of surface defects than zinc or aluminum die casting.

DE 196 06 806 discloses a method and an apparatus for thixotropic metal die casting. The metal alloy, in the form of a pre-prepared billet, is heated to a semi-solid state. It is a state of partial melting, intermediate between the solid state and the liquid state. The alloy prepared in this way is extruded from the cylinders at a flow velocity of 4-15 m / s into narrower feed channels. This increases the flow rate, but remains low. From the feed channels, the melt flows into the mold cavity, where its flow velocity decreases. The alloy does not change in any stage of the process. It remains a semi-solid alloy until it is filled into the mold cavity. Accurate temperature control is necessary to prevent further melting or re-solidification prior to extrusion.

The method of semi-solid pressure casting of magnesium alloy which consists in guiding molten magnesium alloy through a supply channel and injecting into the mold cavity, according to the invention, is characterized in that the melt flow leaving the supply channel is subjected to a controlled lateral expansion with respect to the injection direction. a melt flow velocity in the supply channel is in the range of 140-165 m / s and a melt flow velocity in the controlled expansion area is used which is 25-50% less than the flow velocity of the melt flow in the supply channel.

Preferably, the flow rate of the melt flow in the controlled expansion region is reduced stepwise.

Optionally, the flow rate of the melt stream in the controlled expansion region is decreased progressively.

The melt flow velocity in the supply channel is preferably about 150 m / s.

The flow rate of the melt flow in the controlled expansion area is preferably about 2/3 of the flow rate of the melt flow in the feed channel.

A metal flow system in a magnesium alloy die casting apparatus in a semi-solid state connected to a mold provided with a cavity and having at least one supply channel between a supply of molten alloy and the cavity of the mold, according to the invention, characterized in that the supply channel is connected to each other. at least one controlled expansion area having an increasing cross-sectional area, the ratio of the cross-sectional area of the controlled expansion area to the cross-sectional area of the supply channel is in the range of 2: 1 to 4: 1.

The controlled expansion area is preferably in the infusion of metal directly into the mold cavity.

The controlled expansion area is possibly at least partially inside the mold cavity and is delimited by the surfaces forming the cavity near where the alloy flows into the cavity.

In particular, at the point where the melt flows into the cavity, there is an opening which forms the outlet end of the delivery channel outside the controlled expansion area.

Optionally, there is an infusion at the point where the melt flows into the cavity as part of a controlled expansion area.

In particular, the cross-sectional area of the controlled expansion area increases stepwise with respect to the cross-sectional area of the supply channel.

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Relatively, the cross-sectional area of the controlled expansion area increases progressively with respect to the cross-sectional area of the supply channel.

By using the method and system according to the invention, it is possible to produce good quality pressure castings from magnesium alloys. The castings produced in this way may have a quality comparable to that obtained in the case of castings made of aluminum or zinc alloys. The solutions according to the invention make it possible to significantly improve the casting efficiency, i.e. the percentage ratio of the weight of the casting to the weight of the total metal introduced. As a result, the weight of the metal that needs to be recovered and recycled can be significantly reduced, which means lower production costs.

By casting semi-solid magnesium alloy, filling of the mold cavity is progressively accomplished through semi-solid faces of metal moving from the gate or other insertion point. This form of magnesium alloy filling is a major departure from the highly complex circumferential liquid filling followed by the backfilling encountered in die casting of aluminum or zinc alloys and first described by Frommer in 1932 (see Die Casting, HH Doehler, 1991) , McGraw-Hill Publishing, Inc.).

The controlled expansion region includes an gate through which metal flows from the supply channel into the mold cavity. The actual cross-sectional area for infusion flow is greater than the actual cross-sectional area for flow through the supply channel, whereby the molten metal has a flow velocity in the supply channel greater than the velocity through the infusion. This is contrary to the current recommended practice.

The actual cross-sectional area for the flow through the supply channel may be maintained over the entire length of the supply channel. However, this actual cross-sectional area can only be preserved for part of that length. In the latter case, a larger cross-sectional area may be used for flow through the inlet part of the supply channel.

The area of controlled expansion formed by the cavity may be considered a pseudo-infusion and in general the reference to infusion below should be understood to include both actual infusion and pseudo-infusion.

The embodiments of the invention are suitable for use in hot chamber or cold chamber die casting. In any case, they allow a very large reduction in the production costs of magnesium castings because, as will be shown below, they allow a significant improvement in the casting performance. Since the weight of the riser metal that needs to be recovered and recycled is greatly reduced, a particularly important issue in magnesium casting has been solved.

However, a melt flow velocity in the supply channel in the range 140-165 m / s need not be valid along the entire length of the channel. It is sufficient if this speed is achieved in that part of the supply channel which has a smaller actual cross section than that of the other parts of this channel.

Above, the actual cross-sectional area of flow through the controlled expansion area and through the supply channel is mentioned as being different from the physical cross sectional area of the controlled expansion area and the supply channel. This distinction is important. In solutions with large feed and gates, in accordance with the current best practice of magnesium alloy casting and similar to aluminum and zinc casting, the actual flow path in the feed channels is through a cylindrical area with a cross-sectional area significantly smaller than the physical cross-sectional area of the feed channels. . The much smaller cross-sectional area of the flow area relates to the somewhat centralized core in which the molten metal flows through the feed channels and which is located inside a sleeve of at least partially solidified metal with a significant wall thickness. For a given cross-sectional area of the supply channel, the cross-sectional area of this flow area is greater when the mold is hot.

This difference between the actual cross-sectional area for flow through the supply channel and the physical cross-sectional area for flow through the channel

The feed channel is less pronounced in the feed channel of the present invention. Often this difference can be substantially eliminated. To facilitate this situation, the inlet portion of the supply conduit for the hot chamber system may be formed by a member made of a suitable ceramic material that allows a temperature cycle to be maintained to prevent the metal from solidifying on the surfaces of the member that forms the supply conduit. Alternatively, such an inlet portion of the length of the supply channel of the hot or cold chamber system may be formed by a member adapted to circulate the heat exchange fluid or by the use of an electric heating device.

Hitherto practice has required large supply channel systems with a cross-section larger than the headbox, i.e. the opposite of the present invention for the cross-sections of the supply channel and the controlled expansion area. Consequently, known systems have resulted in a relatively large amount of metal in the riser and thus high costs for the recovery and recycling of the metal from the risers. Hitherto practice has usually resulted in the weight of the metal in the riser being greater than 50% of the weight of the casting, and in some cases more than 100%. That is, the amount of metal in the riser may be greater than in the casting.

Contrary to the known solutions, the solutions according to the invention make it possible to significantly reduce the amount of metal in the riser, so that it constitutes less than 30% of the casting weight in the case of cold chamber machines. In many cases, especially in hot chamber machines, the embodiments of the invention make it possible for the amount of metal in the riser to be significantly less, e.g. about 5% or even about 2%. This is, of course, a considerable practical advantage as the processing cost of the recovered metal is correspondingly reduced.

The solutions of the invention make it possible to significantly reduce the amount of metal in the riser as a direct result of the reduction in cross-section of the supply channel, and the further reduction makes it possible to shorten the length of the supply channel. The cross section can be reduced so that it coincides substantially with the actual flow cross section through the feed channel. However, the actual flow cross-section only needs to be observed over a part of the length of the supply channel, such as a smaller part of that length. Moreover, the portion of the length of the supply channel in which solidification occurs in the casting operation can be significantly shortened to obtain a further reduction of the amount of metal in the riser.

The solutions according to the invention allow significant benefits beyond reducing the cost of recycling. These include significant improvements in casting porosity and surface finish parameters. Compared with aluminum or zinc alloy die casting, magnesium die casting produced by known methods generally has a poorer surface finish, often attributed to porosity at or near the surface of the casting. The solutions according to the invention make it possible to significantly reduce the porosity of the casting as well as to achieve an even surface finish with good quality.

The subject matter of the invention has been illustrated in the embodiments in the drawings, in which fig. 1 is a cross-sectional view showing part of a system according to the invention suitable for the manufacture of door handles, fig. 2 - view of the arrangement of fig. 1, right side, fig. 3 - schematically a cast door handle with attached sprue metal, Fig. 4 - schematic experimental setup, Fig. 5 and 6 - further embodiments of the arrangement, Fig. 7 - schematically filling the mold cavity during magnesium alloy casting, Figs. 8A-8C - cross-sectional shape of the supply channels and schematically for each channel its actual section, Fig. 9 - top view of the cast magnesium alloy bowl, Fig. 10 - section of the bowl from Fig. 9 and a part of the mold along the line XI-XI in Fig. 9, Fig. 11 is a sectional view of a hot chamber die casting mold, and Fig. 12 is a cross section similar to Fig. 11 but showing a modified larger casting suitable for production with the mold of Fig. 11 using a cold chamber machine.

On the other hand, the solutions known from the state of the art are illustrated in the drawings, in which Fig. I shows the known metal flow system, pos. II - schematic filling

190 635 of the mold cavity during casting of a zinc or aluminum alloy, and pos. III-V show experimental metal flow systems.

The subject of the invention is illustrated by a series of examples. The first series of examples aimed to better understand the flow and solidification mechanisms of magnesium alloys. In particular, these examples were intended to determine what improvements in surface finish and porosity levels can be obtained by varying and / or controlling the physical parameters of specific castings.

Some early examples of this first series used the "underflow" technique to understand flow patterns. These examples identified two cavity flow regimes that always gave a poor finish area in between. The flow pattern was not similar to any pattern seen in die-cast zinc or aluminum. Examination of the microstructure showed that:

• The flow in the supply channel was through a cylindrical area with a cross-section much smaller than the designed physical cross-section of the supply channel. It was also noticed in the cross-sections of castings, where the flow was in both directions.

• The percentage of solids in the magnesium alloy castings (demonstrated by long arm spacing dendrites) was approximately 50%.

• The microstructure of the magnesium alloy castings close to the gate differed from that observed at 50-300 mm from the gate.

The results of these initial examples seem to suggest that the metal partially solidified in the feed channel and then the metal behaved as a semi-solid inside the cavity while remaining sticky. The first portion of metal moving along the feed channel (face) appeared to enter the cavity in the liquid state, which could explain the production of different microstructures and the substantially constant position in the casting of the transition between these different flow states.

In the later examples of the first series, changes to the type of runners and gates in the conventional technique resulted in marginally better castings, although major changes were expected. However, the area and location of the poor surface finish remained substantially unchanged. The radical change to a single tapered tangential feed channel gave an extremely good result in terms of casting quality, but the product to riser ratio was unacceptable. However, it appeared that magnesium alloys behaved significantly differently than zinc and aluminum alloys.

The second series of examples were performed with a number of different molds and casting machines to try to determine if the difference in behavior was due to the thixotropy. These examples included various sizes of castings in the range of 15 g - 15 kg and were carried out on both hot chamber machines and cold chamber machines. In one example with a very long casting (about 2 meters) that included a plurality of open ended boxes, the casting was guided along the long edge in a cold chamber machine. Two large supply channels extended from the main filler along partially tapered supply channels. It was found that if the metal was in a thixotropic state in the cavity then it should be possible, due to viscous heating, to fill the casting from one end. To check this, a portion of the previously flooded supply channel was placed in the mold, thereby effectively blocking the flow of metal into this half of the cavity. Any metal in the recess with the blocked feed channel had to enter from the unblocked side, resulting in flow paths in excess of 1 m. The flow path in the recess was very complicated and showed many direction changes. However, without any change to the machine setup, this single-sided feed system produced a casting that was superior in quality at its ends compared to ends produced in a solid feed-through solution. A significant change was noticed in increasing the speed of the metal.

Additional examples of the third series were carried out with a 280 x 25 x 1 mm casting, produced in a small hot chamber machine and fed by a long thin feed channel and very thin 0.15 mm deep gates. These examples showed that the gland was firmly blocked along much of its length, i

190 635 resulted in deterioration of the quality of castings. The supply channel, which was 220 mm long in one direction, was shortened to an effective length of 100 mm by welding a 10 mm-long plug into the supply channel. The resulting casting was completely filled and the metal flowed from the recess into the unlocked part of the inlet channel through a 0.15 mm gate. This proved that the alloy had a very low viscosity the entire time it was filling the cavity. Similar castings of zinc or aluminum alloys would not have this property. The device exerted a pressure of only 14 MPa on the metal.

Examination of magnesium castings made using long, thin gates invariably shows that large portions of the gates are not actually working.

Further examples of the fourth series have been carried out over a range of casting sizes, but all have shown that the quality improves as the gates and feed channels are reduced and the speed of the metal is increased. Examination of the cross-sections of risers in the range from 1 x 1 mm to 50 x 50 mm of a number of castings produced in hot and cold chamber machines showed in each case a central circular area. This property does not appear to be caused by the original shape of the cross-section. For this state, it is assumed to form an area in which metal flows when filling the cavity and is assumed to be the actual flow cross section. Since this area is smaller in cross-sectional area than the feed channel originally cut into the mold, the metal flow becomes much faster. Calculations using the measured metal flow velocities result in velocity values in the supply channel that are approximately 150 m / s, with the infusion velocities being approximately 2/3 of the velocity in the supply channel. Similar areas can be found in castings where there is unidirectional flow.

The fifth series of examples concerned the production of a long, thick casting through progressively smaller gating sections. The infusion length was reduced from 120 mm to 8 mm and the castings were still of acceptable quality. A microbial inspection of the castings showed that the filling was a semi-solid face and the percentage of solids during filling remained constant throughout the part. The porosity was minimal.

In the arrangement 10 of Figures 1 and 2, a mold 12 is shown which forms a plurality of radially extending recesses 14 (only one is shown) in each of which a corresponding door handle having the shape shown in Fig. 3 may be molded. The mold 12 has a fixed portion. 16 and the movable part 17 and is shown closed, but the parts 16, 17 can be separated at the separation line P. The plug 20 included in the mold part 17 has an ejection pin 18 slidably mounted therein. This pin 18 and at least one further pin (not shown) is advanced to eject the casting at the end of each duty cycle.

Opposite the plug 20, part 16 includes a sleeve 22, the bore 22a of which is aligned with the sleeve 24. While the sleeve 22, like the plug 20, is made of suitable steel, such as is used on the parts 16, 17 of the mold 12, the sleeve 24 is preferably made of a material with relatively low thermal conductivity, such as partially stabilized zirconia or other suitable ceramic.

The adjacent ends of the plug 20 and sleeve 22 have a complementary frusto-conical shape. Their ends are such that, with the closed mold 12, the plug 20 and the sleeve 22 are sealed between the abutting opposite end surfaces. The end surface of the plug 20 forms a corresponding groove 21 for each mold cavity 14, the groove 21 cooperating with the end of the sleeve 22 to form a feed channel 26 for the cavity 14. The feed channel 26 is connected to the cavity 14 by a gate 28.

Concentrically with the opening 22a of the sleeve 22, the sleeve 24 forms an opening 24a with a much smaller cross-section. In addition, the outer end of sleeve 22 forms an outwardly projected enlargement of orifice 22a to allow it to engage nozzle 30. The nozzle 30 forms an extension of the S-conduit and plunger (not shown) of a hot chamber die casting system through which molten magnesium can be introduced. through opening 24a into recess 14 through feed channel 26 and gate 28.

Upon completion of the casting cycle in the systems of Figures 1 and 2, the introduced magnesium is solidified all the way to the inner end of bore 24a in sleeve 24. After casting pressure is released, molten metal is expelled through a nozzle 30 from opening 24a.

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In the arrangement of Figures 1 and 2, the length of each supply channel 26 may be minimal. Moreover, each supply channel may have a cross section as small as the actual cross section for the flow of metal through each supply channel 26. The inner end portion of each supply channel 26 is formed by mold parts 16, 17 12. Along this part, the supply channel 26 has progressively decreasing in depth but increasing in width so that the inlet 28 has a narrow, oblong shape with a cross-section greater than that of a portion of the length of the supply channel between the plug 20 and the sleeve 22.

In the arrangement of Figures 1 and 2, the removal of thermal energy to solidify the metal in the supply channel / main gland is accomplished by conduction to the mold parts 16, 17 through the plug 20 and sleeve 22. The relatively short length and cross-section of the supply channels 26 are such that it may not be necessary to circulate the coolant to achieve solidification. However, despite the relatively short length of the supply channel 26 and thus the proximity of the sleeve 24 to the cavity 14, the solidification of the metal in the bore 24a can be prevented by the insulating effect of the ceramic material of which the sleeve 24 is made. The overall arrangement of Figures 1 and 2 is such that when casting magnesium alloy handles having a weight of about 30 g, the length and cross-section of each feed channel 26 are such that the amount of metal in the feed channel / head gate (for two simultaneously cast handles) can be reduced to around 3 g.

Pos. 1 shows a solution similar to that of fig. 1, but belonging to the prior art. In fig. 1, parts corresponding to those of Figures 1 and 2 are referenced as same numerals plus 100.

In the solution presented in Fig. 1, the plug 120 has a frusto-conical pin 120a of a feed channel which, with the mold parts 116, 117 closed, engages in the tapered opening 122a of the sleeve 122. The plug 120 has grooves therein which together with the sleeve 122 form feed channels 126. The plug 120 has also a passage 40 formed therein to circulate a coolant, e.g. water, and the sleeve has a circumferential groove 42 thereabout, the groove 42 being covered by the sleeve 44 to form a further coolant circulation passage 46.

A nozzle (not shown) similar to the nozzle 30 of Fig. 1 is used to allow molten magnesium alloy to be introduced through the opening 122a along the supply channels 126 and into the mold cavity 114 through the filler port 128. After filling is complete, coolant flows through the channels 40,46 to solidify it. metal in the supply channel to the minimum cross section of the opening between the conical pin receiving portion 120a and the flared outer end intended to receive the die of the die casting system.

In the construction of pos. 1, the feed channels 126 are not only longer but also have a larger cross-section. This is to avoid the risk of premature solidification of the magnesium alloy with low heat capacity. For such a door handle casting structure with the same shape and weight as those of Figures 1 and 2, the weight of the metal in the riser is about 30 g. That is, in the structure of Fig. 1, it is necessary to recover 10 times more metal than in the construction of Figures 1 and 2.

Figure 3 schematically shows the magnesium alloy door handle casting 60 withdrawn from its mold cavity and still connected to the metal 62 of the riser. The lug metal 62 is common to the two castings 60, but only one of them is shown and not all of the lug metal for the other cast is shown.

The feed channel in its originally formed state has a designed cross-section of 50 mm ² , and its outer profile corresponds to the shape shown in Fig. 8C and described below. As can be seen from Fig. 8C, the designed cross-section of the supply channel has the shape of a regular trapezoid along the entire length of the channel.

The sixth example was intended to show the effect of the flow of a viscous fluid on the distance traveled by the magnesium alloy during casting. For this purpose, the metal flow system S shown in Fig. 4 was made, consisting of a channel C forming a metal flow path ending in a recess B for a standard tensile test bar. Channel C had a nominal cross-section of 4x4 mm and a length of 1,230 mm.

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The casting trials were carried out with the S configuration of Fig. 4 on a 250 ton cold chamber die casting machine. These tests were carried out under normal machine operating conditions, the mold temperature being only about 120 ° C. As can be seen from Fig. 4, the path of channel C is winding and provides a high flow resistance. Nevertheless, a flow was achieved along the entire length of 1230 mm of channel C, allowing the filling of the rod cavity B to begin. The 1230 mm flow length is not considered a limit. However, this is in contrast to the observed maximum flow length of about 700 mm predicted according to conventional practice using a feed channel cross-section much larger than 4x4 mm.

The seventh series of examples were carried out with the door handle castings 60 of Fig. 3 to determine the minimum size of the supply channels and gates that allow the production of sealed castings. The composition of the kit used in the example was as follows:

• Frech 80 tons hot chamber machine with smelting furnace connected to the tank furnace via a siphon pipe. This meant a constant temperature of the metal.

• DieMac alloy injection monitoring system that determined piston stroke, velocity and pressure.

• Two thermocouples in a fixed mold half, both 7 mm from the face of the cavity and 10 mm and 80 mm from the gate leading to the casting cavity.

• Sheet recorder for displaying temperatures as a function of time.

• Contact thermocouples for measuring surface temperature. • Digital infrared temperature sensors.

• A fully equipped workshop for making mold changes and preparing inserts.

The following examples of the seventh series were conducted at an infusion velocity of approximately 100 m / s:

i) Feeding at the end of casting 60 with a 2 x 1mm filler resulted in castings that were of reasonable quality but not salable. The riser was approximately the same weight as the casting (50% efficiency).

ii) Feeding at the end of the casting with a 7x2mm filler resulted in high quality and salable castings. Brazing was observed in one area, but was overcome by adding a cooling spray in this area, which caused the mold temperature to decrease. Sectioning of the supply channel resulted in a cylindrical flow distribution (described with reference to Fig. 8C) which represented the actual velocity in the supply channel of 150 m / s. If then the actual diameter of the feed channel is reduced to about 3mm (this is the observed diameter of the cylindrical section), the introduction of a physical hole of 3mm should have no effect on the quality of the casting. A portion of the feed channel has been taken to form a segment 64 into which a 3mm diameter hole 64a is drilled to form a 3mm diameter flow channel. Segment 64 introduced in the supply channel adjacent the filler cap so that its hole 64a formed a part of the length of the runner along which it had a reduced cross-section, where the actual cross-sectional area for the flow of metal was not more than 7.1 mm ^2. In this example also a number of short shots were made with a reduction in the amount of metal introduced into the cavity. These short injections with not enough metal have formed a skin that can be caused by metal impact. Due to the high infusion speed of 100 m / s, this could be due to either a liquid flow or a semi-solid material flow.

iii) Normal feed conduit was used but a segment 64 having a 3mm diameter opening 64a was inserted into the 7x2mm infusion feed conduit. The casting was of relatively high quality with little porosity as found from the cross section. Some of the surface markings in the area furthest from the infusion suggested that the flow might have been relatively slightly disrupted. This was done for six shots with normal production in between to maintain the mold temperature. The sharp inlet and outlet of the 3mm bore could have contributed to the drawbacks. No pressure needed to push

190,635 metal through the feed channel and infusion was approximately 20% larger than in normal production.

iv) In a further example, a 7x2mm infusion was inserted with a longer length of A-length supply channel with a 3x3mm channel cut in one side. This section of the supply channel has a cross section 66a cut out; the channel is marked with 66a. The inlet section and the outlet section of the supply channel section were balanced to ensure low flow resistance. The quality of the casting was very good and ensured tight closures of the casting. The pressure needed to push the metal through the feed channel and into the cavity was approximately 30% greater than normal. One sprue of the cast fabricated with the insert in the feed channel was cut and the metal appeared to flow through the section with minimal solidification along the channel walls. It was calculated that the speed through the supply channel was 150 m / s and 100 m / s in the infusion.

v) In another example, a full length B and 3x3mm delivery channel was used to feed a 7x2mm infusion with a total flow length of 120mm over a 3x3mm section. Due to the reduced amount of metal in the area of the supply channel, water cooling of this channel has been eliminated. The casting was of exceptionally good quality. The quality of this casting was considered to be superior to all the others previously obtained. In this case, there were no surface defects noted in example iii) of this series. The pressure needed to fill the cavity was 30% higher than normal. The yield was 94%.

The molten metal entering the supply channel appears to solidify rapidly on the surfaces of the supply channel to form its own channel. If the metal in this central region is semi-solid, then a rapid increase in speed will occur when the percentage of solids is greater than about 50%. If the high speed is maintained then heating due to the viscosity will occur, preventing further heat being dissipated to the mold walls. The metal can therefore flow over long distances. In each of the feed channels used in this work, without any alteration of the machine orientation, the equivalent feed channel gave a metal velocity of 150 m / s. When the feed channel section was inserted into the mold, the speed in the feed channel was initially set at 150 m / s. The quality of the casting should be at least equivalent to that of the casting produced under normal conditions. The improved quality observed may be due to the rapid equilibrium speed of 150 m / s in the supply channel and the speed of 100 m / s in the infusion. Such a reduction in speed prior to reaching the cavity may be utilized such that the speed is decreased from the supply channel through the gate to the cavity.

The best delivery channel design previously was one that had a speed continuously increasing along the flow path so that no air entrapment could occur at the fragmenting metal face. The velocity in the supply channel was no greater than 50% of the rate of the infusion for the greater part of the channel. The detailed results presented here show that high speed can be applied in the feed channel with a corresponding improvement in the quality of the casting.

The solution of Figs. 5 and 6 will be understood in view of Figs. 1 and 2, and parts corresponding to those of Figs. 1 and 2 have the same reference numerals, plus 200 for Figs. 5 and plus 300 for Figs. 6.

The construction of Fig. 5 differs from that of Figs. 1 and 2 in that the opening 224a of the ceramic sleeve 224 is of a different diameter to facilitate clean separation of drawn molten metal from solidified metal in the supply channel. For the greater part of its length than its outer end, the opening 224a has a large diameter in which a correspondingly larger amount of molten metal can be held in the liquid state. Thereafter, the opening 224a is reduced to its minimum diameter over a short length and further increased to its inner end to an intermediate diameter. Where the removal of thermal energy to cause the metal to solidify in the feed channel is such as to cause some solidification at the opening 224a, the structure of FIG. 5 is effective in limiting the degree of this effect. That is, solidification must not progress beyond the short section of minimum diameter, with the least amount of time available in the casting cycle, due to the heat energy contained in the mass of metal in the large outer end portion of opening 224a.

The embodiment of Fig. 6 has advantages similar to that of Fig. 5, with the separation of the solidified metal and the still molten metal taking place with a minimum bore diameter 324a of the ceramic sleeve 324. The design is however advantageous due to the generally simpler form. As shown, the sleeve 322 and sleeve 324 have parallel end surfaces which, when the mold 312 is closed, rest against each other on the mold parting line. Compared to the solution presented in Fig. 1, significant savings of metal remelting can be achieved, up to about 95%.

In fig. II and 7 show schematically the model of filling the mold cavity with zinc or aluminum alloy, in the case of Fig. II and magnesium alloy using the embodiment of the present invention in the case of Fig. 7. These arrays show the respective forms 70a and 70b with the portions 72a, 74a and 72b. 74b that form the mold cavity 76a and 76b and are separated at the parting plane P. The molten alloy may be introduced into the respective cavity 76a, 76b in each case via a metal flow system that includes a feed channel 78a, 78b and a feed gate 80a, 80b.

In fig. II, supply channel 78a has a large cross-sectional area compared to the volume of recess 76a, and molten alloy is introduced from supply channel 78a through gate 80a with a smaller cross-section. The melt flow, represented by the dotted area, conforms to the conventional filling system used in the casting of zinc and aluminum alloys. Stream 82 of alloy is introduced through recess 76a into an area of the recess remote from gate 80a with peripheral melt flow 84 then backfilling the recess. Despite such complex circumferential filling and refilling, good quality castings can be obtained from zinc and aluminum alloys. However, as noted above, this complicated filling produces less than optimal quality magnesium alloy castings.

In Figure 7, supply channel 78b has a small cross-section compared to the volume of the recess 76b. The molten magnesium alloy is introduced from supply channel 78b through gate 80b with a larger cross-section. The cross section of the gate 80b, in addition to being larger than that of the feed channel 78b, may also be larger than the cross section of the gate 80a in FIGS. II for a given volume of the mold cavity. The flowing magnesium alloy, again marked with the dotted area, is in a semi-solid state. In this state, the flowing melt forms a body 86 of alloy that expands away from gate 80b to produce a semi-solid face 88 that moves from gate 80b to the distal regions of recess 76b.

A range of cast shapes and dimensions have been used in the examples detailed herein. As reported, these experiments were performed with hot chamber machines as well as with cold chamber machines. In both cases it has been found that filling the mold cavity proceeds essentially as described with reference to Fig. 7. However, it appears that a small amount of the initial amount of magnesium alloy has entered the cavity in at least some of the castings in a more liquid than semi-solid state. This initial amount, where indicated, was evident from the skin section adjacent to the infusion with a slightly different microstructure (but otherwise of good quality) than the rest of the casting.

The flow described with reference to Fig. 7 was achieved where the melt flow velocity is 140-165 m / s, preferably about 150 m / s, in the feed channel and 25-50% less, e.g. about two-thirds of the flow velocity in the feed channel. by infusion. As stated, this is achieved in the region of a cylindrical core extending through the feed channel as shown in Figures 8A-8C. Each of these drawings shows a cross-sectional view of the respective feed channels 90a, 90b and 90c. The solidification of the alloy in the feed channel after the casting operation is completed and the severing of the riser to provide such a cross-section is represented by such an area 92a, 92b and 92c of the cylindrical core, respectively. These regions represent, for each feed channel, an actual flow channel to which melt flow has been restricted substantially throughout the filling of the mold cavity during the casting operation. Such a limitation exists after a short initial flow time in which alloy 94a, 94b and 94c have at least partially solidified, such as

190 635 is marked by hatching, is formed on the surfaces defining the cross-sectional profile of the supply channel.

The cylindrical shape of the flow regions 92a, 92b and 92c has been found to be a well defined circular section, independent of the profile of the feed channel in which it is formed. Figures 8A-8C show typical supply channel profiles where regions 92a, 92b, and 92c are obtained with circular cross-section. It is apparent from these profiles that the cross-sectional area of the designed supply channel profile can be reduced without significantly affecting the cross-sectional area of the areas 92a, 92b and 92c, but with a reduction in the amount of metal in the resulting supply channel. The amount can be further reduced, preferably as detailed in detail, by reducing the design length of the supply channel. The details given below illustrate to what extent this reduction can be achieved.

A magnesium alloy casting 1.6 kg in the shape of an open frame structure 450 mm high and 400 mm wide with a wall thickness of 2-20 mm and having very deep sections was produced with a cold chamber machine. When using a conventional feed channel mold, the amount of metal in the riser was 1.1 kg, such that a casting yield of 60% was achieved based on the percentage of metal used in the casting operation. This means that about 40% of the metal used had to be recovered. When using a feed channel as in the invention, the amount of metal in the riser was 0.36 kg, which gives a yield of 82% and a reduction of about 67% in the amount of alloy to be recovered.

Door handle castings, as shown in Fig. 3, were produced on a hot chamber machine by casting into two cavities. Each handle had a weight of 28 g, giving a product weight of 56 g per one casting cycle. When manufactured using the conventional metal flow system, 30 g of metal remained in the boss each cycle resulting in a yield of 65%. By applying the solution according to the invention, as shown in Fig. 6, the amount of metal in the riser was reduced to 1.5 g, which gives an efficiency of 97%, and the amount of recovered alloy was reduced by 95% compared to the conventional design.

The eighth series of examples were carried out to determine whether a direct flow of metal into the mold cavity is possible as in normal practice and to determine the effect of a number of alternative metal flow systems. In these experiments, a soap dish-shaped mold cavity was used. This shape of the cavity results from a top view of the cast pan D shown in Fig. 9 and a section through the cup D and the insertion part T of the mold which is shown in Fig. 10 along line XI-XI of Fig. 9. The bowl D has a length of approximately 140 mm. , a width of about 100 mm, a depth of about 26 mm, and a wall thickness of about 2 mm. It has a horizontal circumferential flange and side walls that are inclined at 45 ° with respect to the flange and the flat base.

A conventional procedure for manufacturing the cup D would be to use a metal flow system including a main supply channel for supplying tapered tangential supply channels that extend in opposite directions along a common side edge of the mold cavity and lead along their lengths through a long thin gate into the cavity. In a first attempt, a modified version of the current best practice is represented by the flow system 410 shown in FIG. III. As shown, system 410 has a main supply channel 412 that leads into two opposing tangential supply channels 414 that extend along side edge 416 of the mold cavity to form the cup D of Figure 10. Each supply channel 414 leads to two wedge-shaped or fan-shaped gates 418 that extend across the recess. Each gate 418 has a cross section ranging from about 6 x 1 mm at its feed channel to about 10 x 0.5 mm at the edge 416 of the cavity. In best practice at present, each feed conduit 414 has a normal cross section that tapers in the direction of metal flow along the conduit from 10x10mm to 8x10mm. With such feed channels 414 and heads 418, it would be extremely difficult to manufacture the cup D of an appropriate quality. However, as noted above, system 410 is modified.

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The modification consists in reducing the nominal cross-section of the supply channels 414 to 3 x 3 mm. This modification is in part in accordance with the present invention as far as the cross section of the supply channel is concerned. However, the cross section of the supply channel is greater than that of each gate 418. The system 410 of FIGS. III, despite modifications, does not give satisfactory castings.

In a second construction of this eighth series of examples, the system 420 of FIGS. IV. This arrangement differs from that of 410 in Fig. III in that only one chisel-shaped inlet 428 was used. As shown, gate 428 is at an angle of approximately 45 ° to its feed channel 424 at the end of feed channel 424 and at the edge of recess 426, but faces an adjacent end edge of the recess. The gate 428 has a nominal cross section of 1.5 x 4 mm, so that it is also less than 3 x 3 mm of the nominal cross section of its feed channel 424 (and second blank feed channel 424).

If the gate 428 of system 420 were to provide a directional flow of magnesium alloy as in normal practice, system 420 would be completely unsatisfactory. That is, the flow of metal from gate 428 would be along the adjacent end to the remote side of the cavity, along the distal side to the other end, along the other end to the proximal side having edge 426, and along the proximal side to the gate 428. Poor filling of the central region of the cavity, however, is achieved. the mold would cause unsatisfactory casting quality. However, system 420 was developed to produce better castings for bowl D than that of system 410 in Fig. III.

In the third construction of the eighth series of examples, a system 420a is used as shown in FIG. V. Arrangement 420a differs from arrangement 420 in FIG. IV only in that the chisel gate 428a is positioned at a 90 ° angle to its feed channel 424a and therefore parallel to the adjacent end edge of the cavity. As in system 420, the gate 428a had a nominal cross section of 1.5 x 4 mm so that it was less than 3 x 3 mm of the nominal cross section of its feed channel 424a (and second blank feed channel 424a). The system 420a enables to obtain castings of significantly better quality.

The flow distributions obtained in each example of the eighth series are such that the flow of magnesium alloy into the cavity is not directed. That is, the mold cavity filling pattern is completely dissimilar to that described with reference to pos. II, but where possible the flow is as described with reference to Fig. 7. In the test of Fig. III, a satisfactory flow could not be achieved due to the lack of an adequate controlled expansion area. In the case of the sample presented in Fig. IV, and even more clearly in the case of the sample presented in Fig. V, such an area existed. In any event, however, this area was formed in the mold cavity rather than by the gate 428 of Fig. IV or infusion 428a from ref. V, the area being delimited on three sides by the top and bottom surfaces of the mold cavity and the adjacent end peripheral surface of the cavity. Moreover, in the case presented in Fig. IV, the effectiveness of the expansion area in the mold cavity appears to be reduced, resulting in deterioration in the quality of the casting due to turbulence caused by the flow directed to the adjacent end of the cavity.

In the systems of pos. IV and pos. V, neither the gate 428 nor the gate 428a is in fact an infusion as in the present invention since it does not provide an area of controlled expansion. Indeed, with respect to delivery channel 424 or delivery channel 424a, it restricts flow, such an area as is obtained outside each of the gates 428 and 428a. Therefore, in the sense of the present invention, it is more suitable to consider the gates 428 and 428a as an end portion of supply channel 424 and supply channel 424a leading directly to the controlled expansion area, and consequently there is no infusion there.

Returning to Fig. 10, the principle of the ninth example is illustrated here, which, like the eighth example, was intended to produce magnesium alloy cast cups D. Fig. 10 shows a metal flow system 430 in accordance with the present invention. Arrangement 430 shows the end portion of the flow path of the magnesium alloy which includes a feed passage 434 having a circular cross section having a diameter of 3 mm, which is connected to the mold cavity via a T member.

190 635 through the gate portion 438. From the feed channel 434, the gate 438 increases in diameter in the flow direction and has a diameter of 5 mm at its outlet end at the mold cavity.

As in the eighth example, the bowl D manufactured in the arrangement of Fig. 10 was cast in a cold chamber machine. The system 430 represents a radical departure from known diecasting techniques and would not be used in accordance with current best practice. Nevertheless, system 430 resulted in the production of high-quality magnesium alloy cups D over successive casting test runs, making it generally suitable for fast, repeatable industrial scale casting.

As in the ninth example, the tenth example was intended to produce a magnesium sprue cast by direct feeding through the pin gland. In this case, as shown in Fig. 11, a large casting 440 with wide flat surfaces 440a and a difficult box shaped area 440b with transverse ribs 440c and a head 440d was produced on a Frech 80 tons hot chamber machine. The design area of the casting 440 was 390 cm ² , i.e. it was greater than that recommended by Frech for this machine. '

Casting 440 in Fig. 11 was intended to verify the effect of flow distance and flow properties in a complex shape. Feature 442 used to create the mold cavity for casting 440 was a three-plate mold that allowed direct casting through a single pin gland 448. However, feature 442 also produced a cast 440 or casting 450 with a larger shape than shown in Figure 12 using three pin gates. 448, 448a and 448b on a Toshiba 250 ton cold chamber machine.

Satisfactory castings were produced as shown in Fig. 11. However, the directionality was not controlled within the normal expectation for die casting. The actual flow showed many separate endless fill patterns consistent with previous experiences and similar to those found in plastic molding. There were elongated flow lengths that were in very good agreement with the observations in the sixth example. The flow through the complicated shape of riser 440d also showed a similarity to plastic molding in direct contrast to the flow during pressure die casting.

In the tenth example, there was no pouring of the mold despite the large and complicated shape of the mold being produced. This and other observations indicate that the cast magnesium alloy does not behave like a classical liquid. A further conclusion from this tenth example is that the pressure in the mold cavity was significantly less than that expected for the magnesium alloy in its molten state, i.e. liquid. Even at full injection pressure into the machine, the casting with a designed surface area of 390 cm2 does not flow out, even though the nominal impulse filling force (assuming liquid) is greater than the stated locking force of this Frech machine.

The tenth example in particular highlights the further practical advantages achieved with the present invention. No flow out means that the nominal impulse fill force, i.e. the force expected in the liquid, is significantly greater than the actual force in the inventive magnesium alloy casting process. Consequently, larger castings than expected can be produced on a given machine.

The flow distance and the quality of the casting obtained using the solution of the invention appear to be relatively independent of the mold temperature. However, there may be areas of the mold in hot chamber casting where both heating and cooling must be provided. For both the direct feed in the ninth and tenth examples and at the feed channel in the eighth example, the molten metal must solidify at a point that allows the part to detach from the mold, but also allows the molten metal to flow back into the S-shaped channel. in normal high pressure die casting, a coolant and a heating medium must be used before entering the mold to affect the result. The method employed will depend on the design and size of the machine, as well as the complexity and size of the mold.

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Publishing Department of the UP RP. Mintage 50 copies. Price PLN 4.00.

Claims (12)

Patent claims A method of pressure casting magnesium alloy in a semi-solid state, which consists in guiding molten magnesium alloy through a supply channel and injecting it into the mold cavity, characterized in that the melt flow leaving the supply channel (26) is subjected to a controlled lateral expansion with respect to the injection direction, wherein a melt flow velocity in the supply channel (26) is used in the range of 140-165 m / s and a melt flow velocity in the controlled expansion area is used 25-50% less than the flow velocity of the melt flow in the supply channel (26) . 2. The method according to p. The method of claim 1, wherein the flow rate of the melt flow in the controlled expansion region is reduced stepwise. 3. The method according to p. The process of claim 1, wherein the flow velocity of the melt flow in the controlled expansion area is reduced progressively. 4. The method according to p. The method of claim 1, wherein the melt flow velocity in the feed channel (26) is about 150 m / s. 5. The method according to p. The method of claim 1, wherein the flow rate of the melt flow in the controlled expansion area is about% of the flow rate of the melt flow in the feed channel (26). 6. A metal flow system in a magnesium alloy die casting machine in a semi-solid state connected to a mold provided with a cavity and having at least one supply channel between the molten alloy supply and the mold cavity, characterized in that the supply channel (26) is connected to the cavity. with at least one controlled expansion area with increasing cross-sectional area, the cross-sectional area ratio of the controlled expansion area to the cross-sectional area of the supply channel (26) being in the range of 2: 1 to 4: 1. 7. The system according to p. The method of claim 6, characterized in that the controlled expansion region is a metal inlet (28) directly into the cavity (14) of the mold (12). 8. The system according to p. The process of claim 6, characterized in that the controlled expansion area is at least partially inside the cavity (14) of the mold (12), and is delimited by the surfaces forming the cavity (14) near where the alloy flows into the cavity (14). The system according to p. The method of claim 8, characterized in that at the point where the melt flows into the recess (14), there is an inlet (28) constituting the downstream end of the supply channel (26) outside the controlled expansion area. 10. The system according to p. The method of claim 8, characterized in that at the point where the melt flows into the recess (14) there is an infusion (28) which forms part of the controlled expansion area. The system according to p. The method of claim 6, characterized in that the cross-sectional area of the controlled expansion region increases stepwise with respect to the cross-sectional area of the supply channel (26). 12. The system according to p. The method of claim 6, characterized in that the cross-sectional area of the controlled expansion area increases progressively relative to the cross-sectional area of the supply channel (26).